Expandable functional TFE copolymer fine powder, the expandable functional products obtained therefrom and reaction of the expanded products

ABSTRACT

A functional TFE copolymer fine powder is described, wherein the TFE copolymer is a polymer of TFE and at least one functional comonomer, and wherein the TFE copolymer has functional groups that are pendant to the polymer chain. The functional TFE copolymer fine powder resin is paste extrudable and expandable. Methods for making the functional TFE copolymer are also described. The expanded functional TFE copolymer material may be post-reacted after expansion.

FIELD OF THE INVENTION

Expandable TFE copolymer fine powder resins containing functionalmonomers, expanded functional products obtained from these copolymers,and processes for making them are described herein. Further describedare post-expansion reactions of the expanded functional TFE copolymermaterials, and products made therefrom.

BACKGROUND OF THE INVENTION

Polytetrafluoroethylene or PTFE is known to have a unique combination ofproperties including excellent chemical resistance, thermal stability athigh temperature, low surface energy and excellent electrical(dielectric) properties. PTFE is also known to have two deficiencieswhich limit its use: high cold flow or creep and poor resistance toionizing radiation.

Stretching certain forms of PTFE to make microporous expanded PTFE(ePTFE) can improve strength, decrease cold flow or creep, and improvethe dielectric properties without changing surface or chemicalproperties. The chemical resistance or inertness, as well as the lowsurface energy, of PTFE and ePTFE are beneficial properties for someapplications. But for other applications, it would be beneficial toselectively modify these properties without degrading the polymer.

There has been significant research to modify the surface or chemicalproperties of PTFE and microporous ePTFE in order to improve adhesionand compatibility with other materials. For example, efforts haveincluded attempts to decrease creep by radiation crosslinking, increaseor decrease the surface free energy (e.g. increase or decreasehydrophilicity), and provide sites for chemical reactions to improve theutility of PTFE and/or ePTFE in specific applications by chemical andplasma treatments.

Recently, plasma treatment of microporous ePTFE in the presence ofmaleic anhydride is reported to have produced acid functionality on thesurface of the microporous ePTFE. Though the exact mechanism of thesesurface reactions is not reported, it likely results from the formationof free radicals by bond scission. Where carbon-carbon bond strength isknown to be about forty percent lower than carbon-fluorine bonds, amajority of the radicals would result from scission of the carbon-carbonbonds, or main polymer chain scission, thereby decreasing the molecularweight of the polymer, and restricting the anhydride or acidfunctionality to the ends of the degraded polymer chains. Plasma graftpolymerization is restricted near the surface of the sample. (PlasmaSurface Modification and Plasma Polymerization; N. Inagoki, TechnomicPublishing, 1996, p. 44).

Techniques for dispersion polymerization of both tetrafluoroethylene(TFE) monomer and TFE copolymers have been described. There arereferences which define and distinguish TFE copolymers based on theconcentration of the comonomer. TFE polymers containing less than 1weight percent comonomer have been referred to as modified homopolymers,or modified PTFE, whereas TFE polymers containing more than 1 weightpercent comonomer have been referred to as TFE copolymers.(Fluoroplastics—Vol 1: Non-Melt Processible Fluoroplastics; WilliamsAndrew, Inc., Norwich, N.Y., at p. 19 (2000).) However, for use herein,TFE polymers containing one or more comonomers at any concentration willbe defined as TFE copolymers.

In some processes, dispersion polymerization of TFE produces a resinthat has come to be known as “fine powder.” (e.g., U.S. Pat. No.4,016,345 (Holmes, 1977)). Generally, in such processes, sufficientdispersing agent is introduced into a water carrier such that, uponaddition of TFE monomer in the presence of a suitable polymerizationinitiator and, upon agitation and under autogenous TFE pressure of 10-40kg/cm², polymerization proceeds until the desired level of colloidallydispersed polymer particles is reached and the reaction is then stopped.The dispersed polymer particles may subsequently be coagulated by knowntechniques to obtain the fine powder form of the polymer. The finepowders are dried at temperatures from about 100 to 200° C.

Fine powder resins are known to be useful in paste extrusion processesand in stretching (expansion) processes in which the paste-extrudedextrudate, after removal of extrusion aid lubricant, is stretched toproduce porous, strong products of various cross-sectional shapes suchas rods, filaments, sheets, tubes, etc. Such a stretching process isdisclosed in commonly owned U.S. Pat. No. 3,953,566 (“'566” to Gore).The expansion process as it applies to fluorocarbon polymers isdescribed in the aforesaid '566 patent. As used herein, articles thatcan be the expanded by the process of the '566 patent are said to be“expanded” and the resins used in the expansion process to create sucharticles are said to be expandable TFE polymers or expandable TFEcopolymers.

Dispersion processes to make TFE copolymers are taught in for example,in U.S. Pat. No. 4,792,594 (Gangal et al), U.S. Pat. No. 6,541,589(Baillie), U.S. Pat. App. 2007/0010642 (Sabol and Baillie) and U.S.patent application Ser. No. 11/906,877 (Ford; filed Oct. 4, 2007).Dispersion processes to make copolymers are also described. It is taughtthat fine powders made by these dispersions may be paste extruded andprocessed by the processes disclosed in U.S. Pat. No. 3,953,566 to makemicroporous expanded products. TFE fine powder polymer processed bypaste extrusion or expansion has high crystallinity especially for theportion of polymer formed in the later stage of the polymerization. Thismaterial is sometimes described as the shell or the sheath of thedispersion particle.

TFE copolymers processable by melt extrusion and injection moldinginclude TFE-HFP (hexafluoropropylene) copolymers known as FEP, TFEperfluoroalkyl vinyl ether copolymers known as PFA and MFA, and TFEethylene copolymers known as E-TFE. These polymers are not fine powdersand cannot be paste extruded or expanded into microporous productsbecause of low crystallinity.

TFE copolymers made from fluorovinyl ether comonomers having sulfonylfluoride groups, ester groups and cyano groups have been describedhaving the formulae:CF₂═CF—OR_(f)SO₂F  I.CF₂═CF—OR_(f)COOCH₃  II.CF₂═CF—OR_(f)—CN  III.where R_(f) is fluoroalkyl or fluoroalkyl ether. (Fluoroplastics—Vol. 2:Melt Processible Fluoropolymers; Williams Andrew Inc.; PerfluorinatedIonomer Membranes, American Chemical Society Symposium, Series 180,1982; U.S. Pat. No. 3,692,569 (Grot); Moore, Albert L. FluoroelastomersHandbook, William Andrew Publishing, 2006) Monomers of structures I andII are copolymerized with TFE to form polymers subsequently hydrolyzedto form the sulfonic acid and carboxylic acid. However, these polymerscontain sufficient concentration of comonomer that there is little ifany crystallinity in the polymers. Monomers of structure III have beenpolymerized with TFE and perfluoroalkylvinyl ethers to make perfluoroelastomers where monomer with structure III is the cross link site forthe elastomers. The materials have little or no crystallinity and aretherefore not expandable to create microporous materials.

U.S. Pat. App. 2006/0270780 (Xu et al.) teaches a PTFE modified with acyanovinyl ether cross linking monomer in a microemulsion process. Inthis patent application, the modified PTFE is not a fine powder andcannot be paste extruded and expanded according to the '566 process.

U.S. Pat. No. 7,019,083 (Grootaert) teaches low molecular weight meltprocessable TFE perfluoropropylvinyl ether (PPVE) copolymer containing acyanovinyl ether that is not formed as a fine powder and which wouldlack sufficient crystallinity to be paste extruded and be processed intomicroporous products. U.S. Pat. No. 4,326,046 (Miyaka) teaches makingmodified PTFE by including 0.001 to 10 mol % of a comonomer componenthaving an acid type functional (or precursor to an acid) group. The acidincludes carboxylic, sulphonic or phosphoric acids. U.S. Pat. No.4,326,046, teaches that the particle of the modifiedpolytetrafluoroethylene comprises a core made of homopolymer oftetrafluoroethylene and the modifier component is included in the sheathlayer. U.S. Pat. No. 4,326,046 does not teach paste extruding orexpanding the modified polymer. Materials having the high modifiercomponent polymerized in the later stages of polymerization would nothave sufficient crystallinity to be processed into microporous productsby the '566 process.

U.S. Pat. No. 7,342,066 to Dadalas et al. teaches use of a PTFEdispersion in a coating process. The PTFE contains up to 1 weightpercent of an ionic comonomer (e.g., a monomer having acid groups as anionic group) where at least a portion and preferably all of thecomonomer is added in the later stage of the polymerization. U.S. Pat.No. 7,342,066 does not teach forming a paste extrudable or expandablefine powder. Materials made with the high comonomer concentration at thelater stages of polymerization would have low crystallinity and wouldnot be paste extrudable or expanded by the processes of the '566 patent.

There is a need for TFE copolymer materials containing functional groupswhich impart specific chemical properties to a polymer, wherein thecopolymer can be expanded to provide a microstructure characterized bynodes interconnected by fibrils. There is a further need for expandedTFE copolymer materials containing functional groups that can undergosubsequent controlled reactions to impart other specific properties tothe expanded material while maintaining properties of expanded TFEcopolymer material.

SUMMARY OF THE INVENTION

This invention relates to functional TFE copolymers comprising TFE andat least one comonomer that comprises a functional group. The functionalTFE copolymer has functional groups that are pendant to the polymerchain. The pendant functional groups emanate from a branch in thepolymer chain. The functional TFE copolymer can be expanded (stretchedunder controlled conditions) to produce microporous expanded TFEcopolymer material, having a microstructure characterized by nodes (1)interconnected by fibrils (2) (as exemplified in FIGS. 1 and 2).

A process for polymerization of these monomers to produce functional TFEcopolymers is described, as well as dispersions of the functional TFEcopolymer. Moreover, functional TFE copolymer fine powder is describedthat is paste extrudable and expandable into microporous functional TFEcopolymers. The porous functional products produced by expansion of thepolymers, and reactions of the porous functional TFE copolymericmaterials are described.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 SEM photomicrograph of an expanded sheet of functional TFEcopolymer taken at 10,000× magnification.

FIG. 2 SEM photomicrograph of an expanded sheet of functional TFEcopolymer taken at 10,000× magnification.

DETAILED DESCRIPTION OF THE INVENTION

Described herein are functional TFE copolymers made from an aqueousdispersion polymerization process, and processes for forming finepowders of the functional TFE copolymers that are paste-extrudable andexpandable. The functional TFE copolymer comprises a polymer of TFE andat least one comonomer that contains a functional group. The TFEcopolymers comprise functional groups that are pendant to the polymerchain. A process is provided for making the functional TFE copolymerfine powder from TFE and at least one comonomer containing a functionalgroup. Further described is the microporous expanded TFE copolymerhaving functional groups obtained from the fine powders, and processesfor reacting the microporous expanded TFE copolymer having functionalgroups.

The term TFE copolymer is defined as a TFE polymer comprising one ormore comonomer at any concentration. As used herein the term functionalTFE copolymer is defined as a TFE copolymer having functional groupsthat are pendant to the polymer chain wherein the functional TFEcopolymer is formed by copolymerizing TFE with comonomers having afunctional group. The functional TFE copolymers may be expanded intomicroporous materials. The expanded functional TFE copolymers made bythe processes described herein have a microstructure characterized bynodes interconnected by fibrils and the copolymers have a functionalgroup pendant to the polymer chain.

As used herein, the term functional comonomer is a monomer thatcopolymerizes with TFE in a dispersion polymerization and whenincorporated into the polymer introduces side groups comprisingfunctional groups that are pendant to the polymer chain. Functionalcomonomers which may be useful in this invention include fluorinated andperfluorinated monomers. Fluorinated monomers contain at least onefluorine atom. Perfluorinated monomers have at least one fluorine atom,and no carbon-hydrogen bonds and no carbon-halogen bonds other thancarbon-fluorine bonds. Suitable functional monomers have the generalformulae given in Table 1 where Z is defined as the functional group,examples of which are provided in Table 2.

TABLE 1 General structural formulae for comonomers CX₂═CXZ X: H,halogen, alkyl, fluoro alkyl CX₂═CX—R—Z X: H, halogen, alkyl, fluoroalkyl R: alkyl, alkyl ether, fluoro alkyl ether, perfluo alkyl etherCF₂═CF—O—R_(f)—Z R_(f): fluoro alkyl or fluoro alkyl ether

Functional groups which may be incorporated into the copolymers aspendant groups, include but are not limited to the functional groupslisted in Table 2. As used herein, the term functional groupspecifically excludes ether groups (O—O—C), and groups formed bycarbon-halogen or carbon-hydrogen bonds. These bonds are described as—CX₂— or —CX₃ where X is either halogen or hydrogen. For purposesherein, while chemical moieties including ether groups, and chemicalmoieties formed from carbon-halogen bonds and carbon-hydrogen bonds, arenot considered functional groups, they may be part of a functionalcomonomer comprising a functional group that is suitable for use herein.

TABLE 2 Functional groups alcohols —C—OH aldehydes —CHO ketones —C═Ocarboxylic acids —COOH or salts esters —COOR, —OCOR where R is alkyl oraryl group cyano or nitriles —C≡N amines —C—NH₂, —C—RNH, —C—R₂NR₁ whereR, R₁, and R₂ are alkyl or fluoroalkyl amide

where R₁ and R₂ are alkyl or fluoroalkyl carbonyl halide —XC═O where Xis F or Cl sulfonyl halide —SO₂X where X is F or Cl sulfonic acid —SO₃Hor salts sulfonamide —SO₂NH₂ sulfonimide —SO₂—NHN—SO₂— anhydrides—C(O)—O—(O)C— carbamates O═CONH— sulfides C—S—C cyanate —OC≡N phosphonicO—P(═O)OH₂ triazine

amidine —C(═NH)—NH2 isocynate —N═C═O

The general formulae for comonomers of this invention are given inTable 1. The concentration of the comonomer containing a functionalgroup in the resulting functional TFE copolymers may be less than 5 mol%, or less than 3 mol %, or less than 2 mol %, or less than 1 mol % orless than 0.5 mol %. The concentration of comonomer having a functionalgroup in the resulting functional TFE copolymers may be greater than0.015 mol %, greater than 0.04 mol %, greater than 0.07 mol %, greaterthan 0.1 mol %, greater than 0.5 mol %, greater than 1.0 mol %, greaterthan 2 mol %, or greater than 3 mol %.

The concentration of comonomer containing a functional group in theresulting functional TFE copolymers may be between 0.01 and 5 mol %,0.01 and 3 mol %, or 0.01 and 2 mol %, and can be measured according tothe methods described herein.

At least one functional comonomer may be polymerized with TFE to providea copolymer having a multiplicity of pendant functional groups. Morethan one functional comonomer may also be provided. Where more than onefunctional comonomer is provided, the functional comonomers may providethe same or different functional groups that are pendant to the polymerchain. Additionally, one or more non-functional comonomers may becopolymerized with TFE and the at least one functional comonomer to formthe expandable functional TFE copolymers having pendant functionalgroups. Non-functional comonomers are defined herein as comonomers thatdo not result in pendant functional groups on the polymer chain.Non-functional comonomers include but are not limited to fluoro-olefinsi.e., hexafluoroproylene (HFP), fluoro alkyl vinyl ethers; PMVE(perfluoromethyl vinyl ether), PEVE (perfluoroethyl vinyl ether) andPPVE (perfluoropropyl vinyl ether).

In one embodiment, a functional comonomer comprises a fluorovinyl etherof the general formulaCF₂═CF—OR_(f)Z,where R_(f) represents a fluoro alkyl group optionally interrupted byone or more oxygen(s) and Z represents a functional group from Table 2.Z may be cyano or nitrile, aldehyde, carboxylic acid or salt, ester,amine, amide, carbonyl halide, sulfonyl halide, sulfonic acid or salts,sulfonamide, sulfonimide, anhydride, sulfide, phosphonic acid or salt,hydroxyl (alcohol) sulfate esters, phosphate esters or isocynate.Fluorovinyl ethers monomers may include comonomers listed in Table 3.

TABLE 3 Fluoro Vinyl Ether Functional Comonomers Cyano vinyl ethersCF₂═CFOR_(f)—CN where R_(f) is a fluorinated alkyl or alkyl ether group.Illustrative examples are: CF₂═CF—O(CF₂)_(n)—CN where n = 2-12, orpreferably where n = 2-6; CF₂═CF—O[CF₂—CF(CF₃)—O]_(n)—CF₂—CF(CF₃)—CNwhere n = 0-4, or preferably where n = 0-2;CF₂═CF—[OCF₂CF(CF₃)]_(x)—O—(CF₂)_(n)—CN where x = 1-2, and n = 1-4; andCF₂═CF—O—(CF₂)_(n)—O—CF(CF₃)CN where n = 2-4. One preferred type ofmonomer includes perfluorinated polyethers having a nitrile group and atrifluorovinyl ether group, including perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene), CF₂═CFOCF₂CF(CF₃)OCF₂CF₂CN. Sulfonylfluoride vinyl ethers CF₂═CFOR_(f)SO₂F where R_(f) is a fluorinatedalkyl or alkyl ether group. Illustrative examples are: CF₂═CFOCF₂CF₂SO₂F

One preferred sulfonyl fluoride-containing comonomer isperfluoro(3,6-dioxa-4-methyl-7-octane sulfonyl fluoride),

Acid or ester vinyl ether or other acid precursors

or CF₂═CF—[OCF₂CF(CF₃)]_(m)—O(CF₂)_(n)—(CH₂)_(p)OCOR where R_(f) is afluorinated alkyl or alkyl ether group; m = 0-20; n = 1-10; p = 1-4; andR = alkyl. Illustrative examples are:CF₂═CF—[OCF₂CF(CF₃)]—O(CF₂)₂—CH₂COOCH₃ CF₂═CFO(CF₂)₃CH₂COOCH₃CF₂═CF—OCF₂CF(CF₃)OCF₂CF₂COOCH₃ CF₂═CFO(CF₂)₁₋₈COOCH₃CF₂═CFO(CF₂)₁₋₈COOC₂H₅ CF₂═CFOCF₂CF(CF₃)OCF₂CF₂CF₂COOCH₃

CF₂═CF—[OCF₂CF(CF₃)]—OCF₂CF₂COOH CF₂═CF—[OCF₂CF(CF₃)]—OCF₂CF₂CH₂OPO(OH)₂CF₂═CF[OCF₂CF(CF₃)]—OCF₂CF₂CH₂—OCONH₂ Hydroxyl vinyl ethersCF₂═CF(OCF₂CFCF₃)_(n)O_(p)(CF₂)_(m)CH₂OH where p = 0 or 1; m = 0-10; n =1-20; when m = 0, then p = 0,; and when m > 0, then p = 1. Illustrativeexamples are: CF₂═CF—O—CF₂CF(CF₃)OCF₂CF₂CH₂OH CF₂═CFOCF₂CF₂CF₂CH₂OH

Other comonomers suitable for use in making TFE copolymers describedherein include comonomers listed in Table 4.

TABLE 4 Other functional fluoro monomers CF₂═CFSO₂F CF₂═CFCF₂CF₂SO₂FCF₂═CFCF₂OCF₂CF₂SO₂F CF₂═CF(CF₂)₀₋₈COOCH₃ CF₂═CFCF₂OCF(CF₃)COOCH₃CF₂═CFCF₂OCF(CF₃)CF₂OCF(CF₃)COOCH₃ CF₂═CFCF₂O(CF₂)₄COOCH₃

The polymerization is carried out by an aqueous dispersionpolymerization process to produce a fine powder resin, by modifyingknown processes (e.g., U.S. Pat. No. 4,016,345 to Holmes). The additionof the functional comonomer or optionally other comonomers to thereaction vessel is controlled. Sufficient dispersing agent is introducedinto a water carrier where upon addition of TFE monomer in the presenceof a suitable polymerization initiator, and upon agitation and underautogenous TFE pressure of 10-40 kg/cm², polymerization proceeds untilthe desired level of colloidally dispersed functional TFE copolymerparticles is reached and the reaction is then stopped. The product ofthe polymerization reaction is the functional TFE copolymer dispersedwithin an aqueous colloidal dispersion.

In one embodiment, TFE monomer is pressured into an autoclave containingwater and polymerization initiators, along with paraffin wax to suppresscoagulum formation, and an emulsifying agent. The addition of thefunctional comonomer or optionally other comonomers to the reaction iscontrolled. Where the comonomers are liquid, the process comprisesemulsifying the comonomers prior to adding the comonomers to thereaction vessel. The comonomers are emulsified as emulsions in watercontaining a surfactant, preferably a fluoro surfactant.

Both the amount of functional comonomer added and the starting time ofthe comonomer addition, are determined based on the desiredconcentration of the comonomer in the resulting copolymer and thepolymerization reactivity of the comonomer. The step of adding thecomonomer, including the amount of comonomer added and the time in thepolymerization batch cycle at which the comonomer is added, iscontrolled to assure that the comonomer is essentially completelyreacted or consumed in the polymerization process before thepolymerization is about 80-90% complete. The step of continuingpolymerization, after essentially completely reacting or consuming thecomonomer in the polymerization process, consists of polymerizing TFEfor the final 10-20% of the polymerization in the absence of comonomer.This provides a functional TFE copolymer having high crystallinity ofthe material produced in the last 10-20% of the polymerization. Theresulting functional TFE copolymer resin is paste extrudable andexpandable into microporous structures.

In one embodiment, the process includes removing the comonomer prior to80% to 90% completion of the polymerization, by for example, evacuatingthe comonomer at low pressure or by steam assisted distillation.Subsequently, the polymerization of TFE is resumed and completed.

After polymerization is complete, the process further comprisescollecting the aqueous dispersion of particles which comprises the stepsof lowering the temperature to about 20° C., removing it from wax, andremoving it from the polymerization vessel. The aqueous dispersion isremoved from the polymerization vessel, diluted with water andcoagulated into fine powder by methods known in the art. The fine powderis dried in air or under vacuum at 100 to 200° C. prior to processing bypaste extrusion and expansion.

Known paste-forming techniques can be used to convert the polymer resinto paste form into an article that can then be expanded after removing alubricant. The steps in paste-forming processes include mixing the resinwith a lubricant such as odorless mineral spirits and carrying outforming steps in which the resin is subject to shear.

The paste extrudable functional TFE copolymers made herein areexpandable to microporous structures characterized by having nodesinterconnected by fibrils, for example, by processes taught in U.S. Pat.No. 3,953,566 to make microporous expanded PTFE. Other processes forexpanding the paste extruded resin include but are not limited to thosemethods that are described in commonly owned U.S. Pat. No. 4,902,423, toBacino, U.S. Pat. No. 5,476,589 to Bacino, U.S. Pat. No. 5,814,405 toBranca et al., and U.S. Pat. No. 7,306,729 to Bacino et al.

Dense articles may be formed from expanded TFE copolymer materialsaccording to the methods describing in commonly owned US Pub. No.2008/0061472 to Kennedy et al.

In one embodiment, an expanded microporous functional TFE copolymericmaterial is formed having a microstructure characterized by nodesinterconnected by fibrils wherein the copolymer is a TFE copolymer, andwherein the comonomer comprises functional groups which, in thecopolymer are pendant to the polymer chain. The pendant functionalgroups can impart different properties to the TFE copolymers. Expandedfunctional TFE copolymers, and articles made therefrom, may undergoreactions such as chemical reactions with chemical reactants or reagentsto react or change the functional groups to impart different chemical orphysical properties to the expanded article.

Another aspect of this invention includes a process for reacting theexpanded functional TFE copolymer comprising pendant functional groupswhere at least some of the initial pendant functional groups that resultfrom the polymerization process, form secondary functional groups thatare different from the initial pendant functional groups. Furtherreactions of the secondary functional groups are possible and in someembodiments, for example, may form tertiary functional groups on theexpanded TFE copolymer material to further change the nature of anexpanded functional TFE copolymer material, e.g. to obtain a desiredchemical property.

Organic and biochemistry reactions with the pendant functional groupsdescribed in Table 2 may include reactions between at least some of theinitial pendant functional groups to form secondary functional groups.For example, in one embodiment, a crosslinking reaction comprising thereaction of an expanded functional TFE copolymer comprising threeinitial pendant nitrile groups (—CN) upon heating to a temperature above250° C. forms a triazine structure resulting in crosslinking of the TFEcopolymeric material.

In a further embodiment, at least some of the initial pendant functionalgroups are chemically reacted with another chemical to form secondaryfunctional groups. For example, initial pendant functional groups suchas amide functional groups, acid halide functional groups and nitrilegroups are reacted with water to form acids as secondary functionalgroups, according to the following reactions.—COOR+H₂O→—COOH where R is alkyl or fluoroalkyl;—CONH₂+H₂O→—COOH;—COX+H₂O—COOH where X is halogen;—SOOF+H₂O→—SOOOH; and—CN+H₂O→—COOH

Additional chemical reactions include the reaction of initial pendantnitrile functional groups with ammonia to form amidine groups assecondary functional groups, for example by the following reaction.—CN+NH₃→—C(═NH)NH₂

Further, expanded functional TFE copolymer having pendant functionalgroups comprising an initial ester group can be reacted with otheresters to form a secondary functional group in the form of a differentester group, according to the following reaction.R₁—COOR+R₂—COOR′→R₁—COOR′+R₂—COORwhere R₁ is the initial functional TFE copolymer for example, TFE-EVE(CF₂═CF—OCF₂CF(CF₃)OCF₂CF₂COOCH₃) copolymer, R is alkyl or fluoroalkylgroup and R₂ is an alkyl or fluoroalkyl group and R′ is an alkyl orfluoroalkyl group different than R.

Where the expanded functional TFE copolymer comprises pendant estergroups and/or pendant acid functional groups, the initial functionalgroups may be reacted with ammonia to form amide secondary functionalgroups, according to the following reactions.—COOR+NH₃→—CONH₂—COOH+NH₃→—CONH₂

-   -   where R is alkyl or fluoroalkyl.

Further, an expanded functional TFE copolymer comprising pendant nitrileinitial functional groups can be reacted to reduce the nitrile groups toamine secondary functional groups according to the following reaction.—CN→—CH₂—NH₂

In another embodiment wherein the expanded functional TFE copolymercomprises pendant sulfonyl fluoride initial functional groups that canbe reacted with ammonia to form an expanded TFE copolymer comprisingsulfonamide secondary functional groups, the expanded material can befurther reacted to form sulfonimide teriary functional groups uponheating as follows.—SOOF+NH₃→SO₂NH₂→—SO₂NHNSO₂—

The expanded microporous TFE copolymer material containing pendantfunctional groups provide good media for chemical reactions. Because thefunctional groups are from comonomers polymerized with TFE, the pendantfunctional groups are integrated and may be distributed throughout themicrostructure of the expanded polymeric material. The pendantfunctional groups are surprisingly available for contact with each otheror with additional chemical reagents or reactants. Moreover, thenon-functional part of the expanded microporous structure has highfluorine concentration (equal to or greater than 95 mol % TFE) whichresults in good chemical (solvent) resistance and stability at hightemperatures which make the expanded functional copolymer material agood media for chemical reactions.

In a still further embodiment, the chemical reactants may includenatural and synthetic chemicals that are able to react with pendantfunctional groups of the expanded functional TFE copolymers. Naturalmaterials include biochemicals and biopolymers that include but are notlimited to carbohydrates, carbohydrate polymers or polysaccharides,chitin, glycogen, heparin, polypeptides and proteins, collagen, gelatin,enzymes, nucleic acids, DNA, RNA, lipids, steroids, hormones andpharmaceuticals and other therapeutic agents.

The reactants may also include synthetic polymers. For both natural orbiopolymers and synthetic polymers, the reactive site of the reactantmay also be a functional group that is pendant to the reactant polymerchain. The reactive site of the reactant may alternatively be anon-pendant group. A representative list of synthetic polymericreactants are given in Table 5,

TABLE 5 Representative List of Synthetic Polymeric Reactants andFormulae TFE-PMVE-8CNVE copolymer—(CF₂—CF₂)—[CF₂—CF(OCF₃)]—CF₂—CFOCF₂CF(CF₃)OCF₂CF₂CN TFE-VDF-HFP-8CNVEcopolymer —(CF₂—CF₂)—(CH₂—CF₂)—[CF₂—CF(CF₃)]—CF₂—CFOCF₂CF(CF₃)OCF₂CF₂CNPoly(vinyl acetate) —[CH₂—CH(OCOCH₃)]— Poly(vinyl alcohol) —[CH₂CH(OH)]—Poly(ethylene glycol) HO—(CH₂—CH₂—O)_(n)—H Poly(propylene glycol)HO—(CH₂—CH₂—CH₂—O)_(n)—H Poly(ethylene imine) —(CH₂—CH₂—NH)— Poly(ethylacrylate) —[CH₂—CH(COOC₂H₅)]— Poly(acrylic acid) —[CH₂—CH(COOH)]—Poly(acrylonitrile) —[CH₂—CH(CN)]— Poly(ethylene vinyl acetate)—(CH₂—CH₂)_(m)—[CH₂—CH(OCOCH₃)]_(n)— Poly(ethylene vinyl acohol)—(CH₂—CH₂)_(m)—[CH₂—CH(OH)]_(n)— Poly(acrylamide) —[CH₂—CH(CONH₂)]—Poly(n-butyl isocynate) —[N(C₄H₉)—CO]— Poly(dimethylsiloxane)—[(CH₃)₂SiO]— Poly(lactic acid) —[O—CH(CH₃)—CO]— Poly(methacrylonitrile)—[CH₂—C(CH₃)(CN)]— Poly(L-lactide) —(CH₂—COO)—

In one embodiment, where the synthetic polymer comprises an —OH group,such as in poly(vinyl alcohol) (PVA), the material may be reacted with apendant functional —COOH group of the microporous expanded functionalTFE copolymeric material to form ester bonds that connect the PVA andthe microporous expanded material.

In another embodiment, a —CN group of a terpolymer made from TFE, PMVEand 8-CNVE (i.e., see Table 5) may be reacted with a pendant functional—CN group of the microporous expanded functional TFE copolymer materialto form triazine groups that crosslink the terpolymer with themicroporous expanded material. In a further embodiment, fluoroelastomersthat do not contain cyano functional groups may also be used to reactwith the pendant functional —CN group of the microporous expandedfunctional TFE copolymer material by adding triallylisocyanurate (TAIC)and peroxide to form crosslinking to improve the interface between thefluoroelastomer and the expanded microporous material.

Further, the expanded functional TFE copolymer may be reacted withbiochemical materials such as heparin, a polysaccharide. For example,where the biochemical material comprises hydroxyl —OH, sulfonic acid—SOOOH and carboxylic acid —COOH functional groups, the —OH group may bereacted with pendant carboxylic acid on a microporous expandedfunctional TFE copolymer material to form an ester. The —OH groups mayalso react with an ester group on the microporous material to form a newester group. The —SOOOH group may react with an amine group on themicroporous expanded functional TFE copolymer material to form asulfonamide or sulfonimide. The —COOH group on heparin may react with apendant functional —OH group on the expanded microporous functional TFEcopolymer material to form ester groups. A —COOH group from abiochemical material may also react with an amino group on themicroporous expanded functional TFE copolymer material to form amidegroups.

Test Methods

Break Strength Test of Microporous ePTFE

A process for testing the break strength of a paste extruded andexpanded functional microporous TFE copolymer beading is provided. Thebreak strength associated with an extruded and expanded (stretched) TFEpolymeric beading produced from a particular resin is directly relatedto that resin's general suitability for expansion, and various methodshave been employed to measure break strength. The following procedurewas used to produce and test expanded beading specimens made from thecopolymers of this invention, the data for which are reported hereinbelow.

For a given resin, 113.4 g of fine powder resin is blended together with130 cc/lb (24.5 g) of Isopar® K. The blend is aged for about 2 hours at22° C. in a constant temperature water bath. A 2.54 cm diametercylindrical preform is made by applying about 1,860 kPa of preformingpressure for about 20 seconds. The preform is inspected to ensure it iscrack free. An extruded beading is produced by extruding the preformed,lubricated resin through a 0.254 cm diameter die having a 30 degreeincluded inlet angle. The extruder barrel is 2.54 cm in diameter and theram rate of movement is 50.8 cm/min. The extruder barrel and die are atroom temperature, maintained at 23° C., plus or minus 1.5° C. TheIsopar® K is removed from the beading by drying it for about 25 minutesat 225-230° C. Approximately the first and last 2.5 m of the extrudedbeading are discarded to eliminate end effects. A 5.0 cm section of theextruded beading is expanded by stretching at 290° C. to a final lengthof 127 cm (expansion ratio of 25:1) and at an initial rate of stretch of1000% per second, which is a constant rate of 50.8 cm per second.Approximately a 30 cm length from near the center of the expandedbeading is removed, and the maximum break load of the removed sampleheld at room temperature (23° C. plus or minus 1.5° C.) is measuredusing an Instron® tensile tester using an initial sample length of 5.0cm and a crosshead speed of 5.0 cm/min.

Measurements in duplicate are obtained and reported as the average valuefor the two samples. This procedure is similar to that described in U.S.Pat. No. 6,177,533B1.

Crystallinity Measurements of Expanded Membranes

Infrared spectra were obtained with a Nicolet 550 Series IIspectrometer. The expanded membrane samples were used and scanned for100 scans. The two peaks (about 2363 cm⁻¹ and 778 cm⁻¹) of interest wereused for crystallinity measurements. The degree of crystallinity wascalculated by using the following equation,Crystallinity %=100−(H ₇₇₈/(H ₂₃₆₃×25))where H₇₇₈ is the peak height near wavenumber 778 cm⁻¹ and H₂₃₆₃ thatnear wavenumber 2363 cm⁻¹. The baseline for the peak near 778 cm⁻¹ wasobtained from the line between 754 and 810 cm⁻¹. The baseline for thepeak near 2363 cm⁻¹ was obtained from the line between 2200 and 2600cm⁻¹.Determination of Functional Groups

The Digilab FTS4000 infrared spectrometer was used to determinefunctional groups. FTIR spectra were obtained in the ATR mode by using aPike Technologies MIRacle ATR with a Ge crystal. Wavenumbers foridentifying specific functional groups are given in the examples below.

Determination of Compositions of Functional TFE Copolymers

NMR was used to quantify compositions of functional TFE copolymers. AllNMR measurements were carried out on a Bruker BioSpin Avance II 300 MHzspectrometer operating at a resonance frequency of 282.4 MHz forfluorine-19 with a pulse duration of 3 μs. Spectra were collected atabout 296 K on a Bruker-BioSpin 2.5 mm cross polarization magic anglespinning (CPMAS) probe positioned in a standard bore 7.05 T Bruker ultrashielded superconducting magnet. The samples were positioned at themagic angle and spun at 32.5 kHz. The sample weight for all experimentswas about 10 to 25 mg. The software used for data acquisition and dataprocessing was Topspin 1.3. The ¹⁹F chemical shifts were externallyreferenced to the CF₂ signal of PTFE at −123 ppm.

Thickness Measurements

Thickness was measured by placing the material between the two plates ofa Kafer FZ1000/30 thickness snap gauge (Käfer Messuhrenfabrik GmbH,Villingen-Schwenningen, Germany). The average of the three measurementswas used.

Density Measurements

Density was used to calculate the percent porosity of expanded materialsusing 2.2 g/cc as the full density of the sample. Samples die cut toform rectangular sections 2.54 cm by 15.24 cm were measured to determinetheir mass (using a Mettler-Toledo analytical balance modelAG204) andtheir thickness (using a Kafer FZ1000/30 snap gauge). Using these data,density was calculated with the following formula:

$\rho = \frac{m}{w*l*t}$in which: ρ=density (g/cc); m=mass (g); w=width (cm); l=length (cm); andt=thickness (cm). The average of the three measurements was used.Tensile Break Load Measurements and Matrix Tensile Strength (MTS)Calculations

Tensile break load was measured using an INSTRON 1122 tensile testmachine equipped with flat-faced grips and a 0.445 kN load cell. Thegauge length was 5.08 cm and the cross-head speed was 50.8 cm/min. Thesample dimensions were 2.54 cm by 15.24 cm. For longitudinal MTSmeasurements, the larger dimension of the sample was oriented in themachine, or “down web,” direction. For the transverse MTS measurements,the larger dimension of the sample was oriented perpendicular to themachine direction, also known as the cross web direction. Each samplewas weighed using a Mettler Toledo Scale Model AG204, then the thicknessof the samples was taken using the Kafer FZ1000/30 thickness snap gauge.Three samples were then tested individually on the tensile tester. Theaverage of the three maximum load (i.e., the peak force) measurementswas used. The longitudinal and transverse MTS were calculated using thefollowing equation:MTS=(maximum load/cross-section area)*(bulk density of PTFE)/density ofthe sample),wherein the bulk density of PTFE is taken to be 2.2 g/cc.Bubble Point Measurements

The bubble point and mean flow pore size were measured according to thegeneral teachings of ASTM F31 6-03 using a Capillary Flow Porometer(Model CFP 1500 AEXL from Porous Materials Inc., Ithaca, N.Y.). Thesample membrane was placed into the sample chamber and wet with SilWickSilicone Fluid (available from Porous Materials Inc.) having a surfacetension of 19.1 dynes/cm. The bottom clamp of the sample chamber had a2.54 cm diameter, 3,175 mm thick porous metal disc insert (MottMetallurgical, Farmington, Conn., 40 micron porous metal disk) and thetop clamp of the sample chamber had a 3.175 mm diameter hole. Using theCapwin software version 6.62.1 the following parameters were set asspecified in the table below. The values presented for bubble point andmean flow pore size were the average of two measurements.

Parameter Set Point maxflow (cc/m) 200000 bublflow (cc/m) 100 F/PT (oldbubltime) 40 minbppres (PSI) 0 zerotime (sec) 1 v2incr (cts) 10 preginc(cts) 1 pulse delay (sec) 2 maxpre (PSI) 500 pulse width (sec) 0.2mineqtime (sec) 30 presslew (cts) 10 flowslew (cts) 50 eqiter 3 aveiter20 maxpdif (PSI) 0.1 maxfdif (cc/m) 50 sartp (PSI) 1 sartf (cc/m) 500Gurley Measurements

The Gurley air flow test measures the time in seconds for 100 cm³ of airto flow through a 6.45 cm² sample at 12.4 cm of water pressure. Thesamples were measured in a Gurley Densometer Model 4340 AutomaticDensometer. The average of the three measurements was used.

The following examples are intended to be illustrative of the invention,but are not to be construed as limiting the scope of the invention inany way.

Example 1

A fine powder resin comprising the copolymer of TFE and 8-CNVE wasprepared as follows.

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 kg of paraffin wax, 28 kg of de-ionized(DI) water, 18 g of ammonium perfluorooctanoic acid (APFO) and 5 g ofsuccinic acid dissolved in about 50 g of DI water. The reactor andcontents were heated above the melting point of the wax. The reactor wasrepeatedly vacuumed and pressurized (to about 1 atmosphere or less) withTFE until the oxygen level was reduced to 20 ppm or less. The contentswere briefly agitated at about 60 rpm between vacuum and purge cycles toensure that the water was deoxygenated. 35 g ofperfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene) (8-CNVE)(CF₂═CFOCF₂CF(CF₃)OCF₂CF₂CN), 5 g of 20% APFO, 250 g of DI water wereemulsified by Omni Mixer Homogenizer. To the reactor under vacuum wasadded the above 8-CNVE emulsion as a precharge of comonomer, and thereactor was heated to 83° C. TFE was then added to the reactor until thepressure reached 2.8 MPa, and KMnO₄ in DI water solution (0.063 g/L) wasinjected at 80 ml/min, until about 4 kg of TFE had been added. This wasaccomplished in about 64 minutes. About 320 ml of 20% APFO solution wasadded in 40 ml increments, the first increment being added after about 1kg of TFE had been added to the reactor, and the subsequent incrementsadded after each subsequent 1 kg of TFE had been added, so that thefinal increment was added after 9 kg of TFE had been charged. The KMnO₄addition rate was decreased to 40 ml/min at the 4 kg TFE level andcontinued at this rate until about 6 kg of TFE had been added, at whichtime the addition of KMnO₄ was stopped.

The polymerization reaction was then allowed to continue and thereaction was stopped after about 16 kg of TFE had been added to thereactor. The weight of the dispersion produced was 49.9 kg, and thesolid content of the dispersion was 32.1 wt %. The raw dispersionparticle size (RDPS) of the polymer particles was 0.175 micron.

The polymer dispersion was diluted to about 15 wt % with DI water andthen coagulated with diluted nitric acid (300 ml 65% nitric acid dilutedwith 700 ml DI water) at about 16° C. The ratio of the diluted polymerdispersion to nitric acid was 20 kg dispersion per 100 ml diluted nitricacid. The agitation speed for coagulation was about 275 rpm. Thecoagulum was dried at 130° C. for 18 hours under vacuum. Solid-state ¹⁹FNMR was carried out to characterize the composition of the polymer. Thispolymer contains 0.017 mol % (0.064 wt %) 8-CNVE. The break strength ofthe beading was approximately 42 newtons (N).

Example 2

A fine powder resin comprising the copolymer of TFE and 8-CNVE wasprepared as follows.

The procedures for Example 1 were repeated except that the concentrationof the KMnO₄ solution was 0.1 g/L. The KMnO₄ solution was injected at 80ml/min. until about 4 kg of TFE had been added. This was accomplished inabout 38 minutes. Then the KMnO₄ addition rate was decreased to 40ml/min and continued at this rate until about 6 kg of TFE had beenadded, at which time the addition of KMnO₄ was stopped. The totaladdition time of KMnO₄ solution was about 43 minutes.

The polymerization reaction was then allowed to continue and thereaction was stopped after about 16 kg of TFE had been added to thereactor. The weight of the dispersion produced was 49.2 kg, and thesolid content of the dispersion was 34.5 wt %. The raw dispersionparticle size (RDPS) of the polymer particles was 0.208 micron.

The dispersion was coagulated in the same process as described inExample 1 and dried at 130° C. for 18 hours under vacuum. Solid-state¹⁹F NMR was carried out to characterize the composition of the polymer.This polymer contains 0.019 mol % (0.072) wt % 8-CNVE.

Example 3

A fine powder resin comprising the copolymer of TFE and 8-CNVE wasprepared as follows.

The procedures for Example 1 were repeated except that 52 g 8-CNVE wasadded to 5 g of 20% APFO and 250 g of DI water, emulsified by Omni MixerHomogenizer, and added as a precharge to the reaction. The concentrationof the KMnO₄ solution was 0.1 g/L. The KMnO₄ solution was injected at 80ml/min until about 3 kg of TFE had been added. This was accomplished inabout 63 minutes. Then the KMnO₄ addition rate was decreased to 40ml/min and continued at this rate until about 4 kg of TFE had beenadded. The KMnO₄ addition rate was again increased to 80 ml/min andcontinued at this rate until about 6 kg of TFE had been added, at whichtime the addition of KMnO₄ was stopped. The total addition time of KMnO₄solution was about 86 minutes.

The polymerization reaction was then allowed to continue and thereaction was stopped after about 16 kg of TFE had been added to thereactor. The weight of the dispersion produced was 52.2 kg, and thesolid content of the dispersion was 32.8 wt %. The raw dispersionparticle size (RDPS) of the polymer particles was 0.186 micron.

The dispersion was coagulated in the same process as described inExample 1 and dried at 130° C. for 18 hours under vacuum. Solid-state¹⁹F NMR was carried out to characterize the composition of the polymer.This polymer contains 0.044 mol % (0.17 wt %) 8-CNVE. The break strengthof the beading was 45 N.

Example 4

A fine powder resin comprising the copolymer of TFE and 8-CNVE wasprepared as follows.

The procedures for Example 1 were substantially repeated except that 118g 8-CNVE was added to 5 g of 20% APFO and 250 g of DI water, emulsifiedby Omni Mixer Homogenizer, and added as a precharge to the reaction. Theconcentration of the KMnO₄ solution was 0.15 g/L. The KMnO₄ solution wasinjected at 80 ml/min until about 2 kg of TFE had been added, at whichtime the addition of KMnO₄ was stopped. The total addition time of KMnO₄solution was about 143 minutes. 10.4 kg of KMnO₄ solution was added.

The polymerization reaction was then allowed to continue and thereaction was stopped after about 13.4 kg of TFE had been added to thereactor. The weight of the dispersion produced was 52.8 kg, and thesolid content of the dispersion was 27.9 wt %. The raw dispersionparticle size (RDPS) of the polymer particles was 0.194 micron.

The dispersion was coagulated in the same process as described inExample 1 and dried at 130° C. for 18 hours under vacuum. Solid-state¹⁹F NMR was carried out to characterize the composition of the polymer.This polymer contains 0.13 mol % (0.51 wt %) 8-CNVE. The break strengthof the beading was 47 N.

Example 5

A fine powder resin comprising the copolymer of TFE and PSVE wasprepared as follows.

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 kg of paraffin wax and 28 kg of DIwater, 18 g of APFO and 5 g of succinic acid dissolved in about 50 g ofDI water. The reactor and contents were heated above the melting pointof the wax. The reactor was repeatedly vacuumed and pressurized (toabout 1 atmosphere or less) with TFE until the oxygen level was reducedto 20 ppm or less. The contents were briefly agitated at about 60 rpmbetween vacuum and purge cycles to ensure that the water wasdeoxygenated. 1500 g of perfluoro(8-sulfonic acidfluoride-5-methyl-3,6-dioxa-1-octene) (PSVE)(CF₂═CFOCF₂—CF(CF₃)OCF₂CF₂SOOF), 50 g of 20% APFO, and 1500 g of DIwater were emulsified by Omni Mixer Homogenizer. To the reactor undervacuum 688 g of the above PSVE emulsion was added as a precharge ofcomonomer, and the reactor was heated to 83° C. TFE was then added tothe reactor until the pressure reached 2.8 MPa, and KMnO₄ in DI watersolution (0.063 g/L) was injected at 80 ml/min. until about 4 kg of TFEhad been added. A drop in pressure indicated the start ofpolymerization. TFE was continuously added to maintain the pressure.About 320 ml of 20% APFO solution was mixed with the rest of the PSVEsolution. The mixed solution was added with an increment of 43 ml for200 g of TFE consumed. The first increment was added after about 200 gof TFE had been added to the reactor, and the subsequent increments wereadded after each subsequent 200 g of TFE had been added. The finalincrement was added after 12 kg of TFE had been charged. The KMnO₄addition rate was decreased to 40 ml/min at the 4 kg TFE level andcontinued at this rate until about 10 kg of TFE had been added, at whichtime the addition of KMnO₄ was stopped. This was accomplished in about47 minutes.

The polymerization reaction was then allowed to continue and thereaction was stopped after about 16 kg of TFE had been added to thereactor. The weight of the dispersion produced was 50.5 kg, and thesolid content of the dispersion was 36.6 wt %. The raw dispersionparticle size (RDPS) of the polymer particles was 0.270 micron.

The dispersion was coagulated in the same process as described inExample 1 and dried at 130° C. for 18 hours under vacuum. Solid-state¹⁹F NMR was carried out to characterize the composition of the polymer.This polymer contains 1.9 mol % (8.0 wt %) PSVE. The break strength ofthe beading was 28.5 N.

Example 6

A fine powder resin comprising the copolymer of TFE and EVE was preparedas follows.

To a 50-liter, horizontal polymerization reactor equipped with a3-bladed agitator was added 1.5 kg of paraffin wax, 28 kg of DI water,18 g of APFO and 5 g of oxalic acid dissolved in about 50 g of DI water.The reactor and contents were heated above the melting point of the wax.The reactor was repeatedly vacuumed and pressurized (to about 1atmosphere or less) with TFE until the oxygen level was reduced to 20ppm or less. The contents were briefly agitated at about 60 rpm betweenvacuum and purge cycles to ensure that the water was deoxygenated. 80 gof perfluoro(8-carboxymethyl-5-methyl-3,6-dioxa-1-octene) (EVE)(CF₂═CF—OCF₂CF(CF₃)OCF₂CF₂COOCH₃), 5 g of 20% APFO, and 250 g of DIwater were emulsified by Omni Mixer Homogenizer. To the reactor undervacuum was added the above EVE emulsion as a precharge of comonomer, andthe reactor was heated to 83° C. TFE was then added to the reactor untilthe pressure reached 2.8 MPa, and KMnO₄ in DI water solution (0.15 g/L)was injected at 80 ml/min until about 1 kg of TFE had been added. Apressure drop indicated that polymerization started. TFE wascontinuously added to maintain the pressure. After 1 kg of TFE wasadded, the injection rate of KMnO₄ in DI water solution was decreased to40 ml/min until 3 kg of TFE had been added and then the solution wasinjected at 20 ml/min. Until about 6 kg of TFE had been added, at whichtime the addition of KMnO₄ was stopped. This was accomplished in about15 minutes. About 320 ml of 20% APFO solution was added in 40 mlincrements, the first increment being added after about 2 kg of TFE hadbeen added to the reactor, and the subsequent increments were addedafter each subsequent 1 kg of TFE had been added, so that the finalincrement was added after 9 kg of TFE had been charged.

The polymerization reaction was then allowed to continue and thereaction was stopped after about 16 kg of TFE had been added to thereactor. The weight of the dispersion produced was 45.6 kg, and thesolid content of the dispersion was 35.1 wt %. The raw dispersionparticle size (RDPS) of the polymer particles was 0.232 micron.

The dispersion was coagulated in the same process as described inExample 1 and dried at 180° C. for 18 hours under vacuum. Solid-state¹⁹F NMR was carried out to characterize the composition of the polymer.This polymer contains 0.098 mol % (0.41 wt %) EVE. The break strength ofthe beading was 23.6 N.

Example 7

A fine powder resin comprising the copolymer of TFE and EVE was preparedas follows.

The procedures for Example 6 were substantially repeated except that thereactor was evacuated after 10 kg of TFE had been added into the reactorand then TFE was recharged into the reactor until the pressure of thereactor was 2.8 MPa. Then, the KMnO₄ solution was injected at 80 ml/min.until about 1 kg of TFE had been added. Then the KMnO₄ addition rate wasdecreased to 40 ml/min and after 2 kg of TFE was added, the KMnO₄injection rate was decreased to 20 ml/min until 6 kg of TFE had beenadded, at which time the addition of KMnO₄ was stopped. The totaladdition time of KMnO₄ solution was about 31 minutes.

The polymerization reaction was then allowed to continue and thereaction was stopped after about 16 kg of TFE had been added to thereactor. The weight of the dispersion produced was 46.2 kg, and thesolid content of the dispersion was 35.4 wt %. The raw dispersionparticle size (RDPS) of the polymer particles was 0.238 micron.

The dispersion was coagulated in the same process as described inExample 1 and dried at 180° C. for 18 hours under vacuum. Solid-state¹⁹F NMR was carried out to characterize the composition of the polymer.This polymer contains 0.095 mol % (0.40 wt %) EVE. The break strength ofthe beading was 28.0 N.

Example 8

An expanded functional copolymer comprising the copolymer of TFE and8-CNVE was prepared as follows.

The resin from Example 3 was mixed with Isopar® K (Exxon Mobil Corp.,Fairfax, Va.) at a concentration of 0.217 g/g of resin and formed into apellet approximately 10 cm in diameter at a pressure of about 2070 kPa.The pellet was heated to about 50° C. and paste extruded into a tapehaving dimensions of about 0.076 cm thick and about 15.25 cm widethrough a die having a reduction ratio of about 100 to 1, at a averageextrusion pressure of about 10,300 kPa. The reduction ratio is the ratioof the cross sectional area of the extruder barrel to the crosssectional area of the extrusion die exit. The resultant tape wascalendared at a rate of 50 meters/minute at about 45° C. to about 0.020cm thick and about 15.25 cm wide. The lubricant was removed by heatingat 180° C. to 210° C. The width of the dried tape was about 14.6 cm.

The resultant tape was stretched in the longitudinal direction at about300° C. and 4.5 meters/minute to a ratio of 10:1. The resultant tape wasabout 8.9 cm wide. The resultant tape was stretched transversely at 300°C. at 19.8 meters/minute at a ratio of 7.5:1 and sintered at about 390°C. for about 20 seconds. The resultant membrane was characterized andthe results are given in Table 6. A scanning electron micrograph, at10,000 magnification, of the membrane is given in FIG. 1.

TABLE 6 Properties of Membrane Made in Example 8 Example 8 (fine powderproduced in Example 3) Porosity (%) 85 Mean Flow Pore size (μm) 0.16Thickness (μm) 2.5 Density (g/cc) 0.39 Crystallinity (%) 71 Avg. MatrixTensile 230 Strength (MPa)

Example 9

An expanded functional copolymer comprising the copolymer of TFE andPSVE was prepared as follows.

A resin made in accordance with Example 5 containing 0.76 mol % (3.3 wt%) PSVE was both paste extruded into a tape and stretched in accordancewith the processes of Example 8 except that the lubricant was removed byheating at about 250° C. The extruded tape had a width of about 13 cmand then the tape was paste stretched into a microporous membrane. Theresultant membrane was characterized and the results are given in Table7. A scanning electron micrograph, at 10,000 magnification, of themembrane is given in FIG. 2.

TABLE 7 Properties of Membrane Made in Example 9 Example 9 Mass/area(g/m²⁾ 4.1 Thickness (μm) 2.5 Gurley (sec) 9.6 Bubble Point (kPa) 630Avg. Matrix Tensile Strength (MPa) 230

Example 10

An expanded functional copolymer comprising the copolymer of TFE and8-CNVE was reacted as follows.

An expanded microporous functional TFE copolymer membrane was madeaccording to Example 8, from a PTFE fine powder prepared according tothe process described in Example 3 containing 0.044 mol % (0.17 wt %)8CNVE. The expansion process, carried out at about 300° C. and thenrestrained and heated at about 390° C. in an oven for about 20 seconds,resulted in an expanded microporous membrane containing triazine (about1560 cm⁻¹), a crosslinked structure, and the unreacted cyano group(about 2297 cm⁻¹) determined by FTIR.

Example 11

An expanded functional copolymer comprising the copolymer of TFE and8-CNVE was reacted as follows.

Aminopropyltriethoxysilane (Aldrich) was mixed with a 95 wt % ethanol(Aldrich)/5 wt % DI water solution to yield a 10 wt % silane solution.About five minutes were allowed for hydrolysis and forming the silanolgroups. An expanded functional TFE copolymer membrane made according toExample 8 from a TFE copolymer fine powder containing 0.044 mol % (0.17wt %) 8-CNVE was immersed in the solution for 2 minutes. It was thenrinsed free of excess silane solution by dipping briefly in ethanol andair dried. Curing of the membrane was carried out at 110° C. for 30 min.The reacted membrane became transparent in water, indicating it washydrophilic. The unreacted membrane was white in water, indicating itwas hydrophobic.

Example 12

An expanded functional copolymer comprising the copolymer of TFE and8-CNVE was reacted as follows.

An expanded functional TFE copolymer membrane made according to Example8 from a TFE copolymer fine powder containing 0.044 mol % (0.17 wt %)8-CNVE prepared in Example 3 was first wetted with isopropanol (IPA)(Aldrich) and then immersed in a 28 wt % aqueous ammonium hydroxidesolution (Aldrich) at room temperature for 20 hours. It was then rinsedwith DI water and air dried. The reacted expanded functional TFEcopolymer membrane contains a new group, amidine (about 1743 cm⁻¹),determined by FTIR.

Example 13

An expanded functional copolymer comprising the copolymer of TFE and8-CNVE was cross linked with a fluoroelastomer.

Viton™ GF-S (fluoroelastomer) was compounded with 4 phrtriallylisocyanurate (Aldrich) and 4 phr Luperox™ 101 (Aldrich) on amill; the compounded mixture was dissolved in MEK (methyl ethyl ketone)to form a 20% solids solution. An expanded functional TFE copolymermembrane was made according to Example 8 from a TFE copolymer finepowder made according to the process of Example 3 containing 0.044 mol %(0.17 wt %) 8-CNVE. The membrane was imbibed with the Viton™ compoundand dried at 90° C. Slabs (composite A) having a thickness of about 0.5to 0.76 mm were made by stacking Viton™ imbibed expanded functional TFEcopolymer membrane. Expanded functional TFE copolymer/Viton™ compositewas formed by molding at 180° C. for 10 min followed by post-curing in aconvection oven at 233° C. for 24 hours. Comparative slabs (composite B)were made by a similar process, except that ePTFE membrane was used inplace of expanded functional TFE copolymer membrane and therefore, didnot contain 8-CNVE. The IMASS peel tester was used for peel tests thatwere carried out in the T-peel mode with a 5-lb load cell at a speed of6 in/min. Peel strengths were 2.2 and 1.5 lb/in for composite A andcomposite B, respectively.

Example 14

An expanded functional copolymer comprising the copolymer of TFE andPSVE was reacted as follows.

An expanded functional TFE copolymer membrane made by the processingconditions of Example 9, was made from a functional TFE copolymer finepowder containing 1.9 mol % (8.0 wt %) PSVE made according to theprocess of Example 5. The membrane was first wetted with IPA and thenimmersed in a 20 wt % KOH solution (Aldrich) at 100° C. for 24 hours. Itwas then rinsed with DI water and was immersed in 15 wt % nitric acid(Aldrich) at 60° C. for 24 hours. The reacted membrane was rinsed withDI water and dried at 100° C. for 1 hour. The conversion of the sulfonylfluoride group (about 1469 cm⁻¹) into the sulfonic acid group (about1059 cm⁻¹) was confirmed by FTIR.

Example 15

An expanded functional copolymer comprising the copolymer of TFE andPSVE was reacted as follows.

An expanded functional TFE copolymer membrane made by the processingconditions of Example 9, was made from a functional TFE fine powdercontaining 1.9 mol % (8.0 wt %) PSVE made according to the process ofExample 5. The membrane was first wetted with IPA and then immersed in a28 wt % aqueous ammonium hydroxide solution at about 5° C. for 3 hours.The reacted membrane was rinsed with DI water and air dried. Theexpanded functional TFE copolymer membrane was cured by heating at 200°C. for 1 hour. The sulfonimide group (about 1740 cm⁻¹), the crosslinkedstructure, was determined by FTIR.

Example 16

An expanded functional copolymer comprising the copolymer of TFE and EVEwas reacted as follows.

Expanded functional TFE copolymer membrane was made from fine powdermade according to the process of Example 6. This fine powder contained0.098 mol % (0.41 wt %) EVE.

The resin from Example 6 was mixed with Isopar® K (Exxon Mobil Corp.,Fairfax, Va.) at a concentration of 0.207 g/g of resin and formed into apellet approximately 10 cm in diameter at a pressure of about 2070 kPa.The pellet was heated to about 50° C. and paste extruded into a tapehaving dimensions of about 0.076 cm thick and about 15.25 cm widethrough a die having a reduction ratio of about 100 to 1, at an averageextrusion pressure of about 15,000 kPa. The reduction ratio is the ratioof the cross sectional area of the extruder barrel to the crosssectional area of the extrusion die exit. The resultant tape wascalendared at a rate of 8.2 meters/minute at about 45° C. to about 0.015cm thick. The lubricant was removed by heating at 180° C. to 210° C. Thewidth of the dried tape was about 15.8 cm.

The resultant tape was stretched in the longitudinal direction at about250° C. and 15.24 meters/minute to a ratio of 2:1. The resultant tapewas about 13.5 cm wide. The resultant tape was stretched transversely at300° C. at 100% per second at a ratio of 6:1 in the transversedirection.

The membrane was first wetted with isopropyl alcohol and then immersedin a 28 wt % aqueous ammonium hydroxide solution at about 5° C. forthree hours. The reacted membrane was rinsed with DI water and air driedat room temperature. The reacted membrane became semi transparent inwater indicating it was hydrophilic. The unreacted membrane was white inwater, indicating it was hydrophobic.

Example 17

An expanded functional copolymer comprising the copolymer of TFE and EVEwas reacted as follows.

Expanded functional TFE copolymer was made according to Example 6. Thisfine powder contained 0.098 mol % (0.41 wt %) EVE. The fine powder wasprocessed to a membrane according to the processes of Example 16.

The membrane was first wetted with isopropyl alcohol. The pre-wettedexpanded TFE copolymer membrane was immersed in 50 wt % aqueous sulfuricacid and held at 60° C. for 24 hours. The membrane was then rinsed withDI water and dried at 60° C. for 2 hours. FTIR spectra showed thepresence of the carboxylic acid (about 3300 cm⁻¹) functionality, showingat least some of the ester functional group was hydrolyzed to thecarboxylic acid.

We claim:
 1. A functional tetrafluoroethylene (TFE) copolymer finepowder resin comprising: a functional TFE core-shell copolymercomprising: a core comprising a polymer chain of TFE and at least onecomonomer having a functional group pendant to the polymer chain; and ashell consisting of TFE monomers, wherein the at least one comonomerhaving a functional group is present in the copolymer an amount between0.01 mol % and 5 mol % of the functional TFE core-shell copolymer,wherein said at least one comonomer having a functional group isselected from a fluorinated monomer and a perfluorinated monomer, andwherein said functional group is selected from nitrile, aldehyde,carboxylic acid or salt, ester, amine, amide, carbonyl halide, sulfonylhalide, sulfonic acid or salts thereof, sulfonamide, sulfonimide,anhydride, sulfide, phosphonic acid or salts thereof, hydroxy (alcohol),sulfate esters, phosphate esters, or isocyanate.
 2. The functional TFEcopolymer fine powder resin of claim 1, wherein the at least onecomonomer having a functional group present in the copolymer is between0.01 and 3 mol % of the functional TFE core shell copolymer.
 3. Thefunctional TFE copolymer fine powder resin of claim 1, wherein the atleast one comonomer having a functional group present in the copolymeris between 0.01 and 2 mol % of the functional TFE core shell copolymer.4. The functional TFE copolymer fine powder resin of claim 1, whereinthe at least one comonomer having a functional group is a fluorovinylether of the general formula CF₂═CF—OR_(f)Z, where R_(f) represents afluoro alkylene group optionally interrupted by one or more oxygen(s)and Z represents the functional group.
 5. The functional TFE copolymerfine powder resin of claim 4, wherein the at least one comonomer havinga functional group comprises a fluorovinyl ether selected from estervinyl ether, sulfonyl fluoride vinyl ether or cyano vinyl ether.
 6. Thefunctional TFE copolymer fine powder resin of claim 1, wherein the atleast one comonomer having a functional group is selected fromperfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene) (8-CNVE),perfluoro(8-carboxymethyl-5-methyl-3,6-dioxa-1-octene) (EVE), orperfluoro(8-sulfonic acid fluoride-5-methyl-3,6-dioxa-1-octene) (PSVE).7. The functional TFE copolymer fine powder resin of claim 1, whereinsaid core comprises a first comonomer comprising a first functionalgroup and a second comonomer comprising a second functional group. 8.The functional TFE copolymer of claim 7, wherein the second functionalgroup is different from the first functional group.
 9. The functionalTFE copolymer of claim 7, wherein the second functional group is thesame as the first functional group.
 10. The functional TFE copolymerfine powder resin of claim 1, wherein said functional TFE core-shellcopolymer further comprises at least one additional comonomer without apendant functional group.
 11. The functional TFE copolymer fine powderresin of claim 1, wherein said shell is formed during the last 10-20% ofpolymerization of said functional TFE core-shell copolymer.
 12. Thefunctional TFE copolymer fine powder resin of claim 11, wherein saidshell is formed during the last 10% of polymerization of said functionalTFE core-shell copolymer.